1. Field of the Invention
The present invention relates to a stereoscopic retinal camera capable of photographing stereoscopically a fundus of an examinee's eye, and more particularly to a stereoscopic retinal camera comprising a judging mechanism to judge alignment condition of the camera with respect to the examinee's eye and capable of providing a right and a left pictures of uniform picture quality.
2. Description of Related Art
Conventionally, known are simultaneous stereoscopic retinal cameras capable of providing a pair of stereo images of a fundus of an examinee's eye by dividing a light beam reflected by the fundus into two light beams through a two-hole diaphragm and then photographing the divided light beams with right and left photographing optical systems respectively.
Alignment condition of the apparatus with respect to the eye has been judged by an examiner empirically while observing images of the fundus and the anterior surface of the eye through binocular eyepieces and a monitor.
Stereoscopic retinal cameras in the prior art are provided with a direct viewfinder for an observing optical system. Direct viewfinders of various type have been proposed, one of which is capable of observing a right and a left images of the fundus individually through each monocular eyepiece, another one of which is capable of observing the two images of the fundus arranged side by side by transmitting them inside the visual field of the monocular eyepiece, and last one of which is capable of observing the two images of the fundus through binocular eyepiece thereby to provide a stereoscopic vision.
The examiner carries out alignment operation of the apparatus while observing images of the fundus through any one of the direct viewfinders.
In fundus stereo photographing, uniformity in right and left picture images is important for diagnosis and analysis. In the apparatus in the prior art, a photographer has judged uniformity in right and left picture images, particularly uniformity of actual brightness in right and left images by directly observing balance of brightness of the two images.
The former alignment way has an advantage of capable of promptly and simply judging alignment condition, but has difficulty in judging it accurately because the observed images are constantly changing due to blinking or motion of the eye and so on. The examiner, particularly inexperienced, would therefore usually judge alignment to be achieved even when actual alignment is not proper. In the improper alignment condition, photographed picture images have unevenness in light quantity or flare light gotten therein, thereby not providing photographed images with high quality. Accordingly, there is a case where rephotographing of the images is required.
In the latter way with direct viewfinders, judgement on the balance of brightness between the two images is delicate, so that strict adjustment operation of the balance of brightness demands great skill and experience. Particularly, when photographing a fundus of an eye of an old person whose natural mydriasis is not sufficient, with a stereoscopic retinal camera without use of mydriasis, only one of right and left luminous flux is often eclipsed by the pupil of the eye. It is, accordingly, very difficult to adjust balance of brightness in the images.